Illinois Gov. Rod Blagojevich on Monday signed into law a bill that would impose a fine on retailers that sold violent or sexually explicit videogames to minors.

The Entertainment Software Association, meanwhile, sued the state in federal court, claiming that the law violated the constitutional right to free speech. The Video Software Dealers Association and the Illinois Retail Merchants Association joined the ESA in the complaint.

The law, which goes into effect Jan. 1, would fine violators up to $1,000 for each mature-rated videogame sold to minors under 18 years old. The bill also requires retailers to label violent and sexually explicit videogames.

The ESA, which claimed similar bills were struck down by the courts in St. Louis, Indianapolis and Washington state, said the law would have a "chilling effect on free speech."

"It will limit First Amendment rights not only for Illinois' residents, but for game developers and publishers, and for retailers who won't know what games can and cannot be sold or rented under this vague new statute," Douglas Lowenstein, president of the ESA, said in a statement. "I'm confident the court will affirm our position."

Besides the constitutional questions, the law also substitutes the government's judgment for parental supervision and turns retailers in to surrogate parents, the ESA argued. In addition, the law would treat computer and videogames differently from other constitutionally protected works, such as films, music and books.